The Sterilight QS-012 UV Lamp Quartz Sleeve is made of 100% fused silica. The QS-012 Quartz Sleeve is designed to allow high transmittance, giving the UV lamp optimal performance in purifying the water. Open ended quartz sleeve designed for use with Silver, Silver Plus and the GOLD series Sterilight Water Sterilization Systems. Two Replacement O-Rings included.